The disclosed subject matter relates generally to telecommunication and, more particularly, to a method and apparatus for compensating for transceiver impairments.
In telecommunication, direct-conversion techniques involve mixing a baseband signal with a carrier signal without using an intermediate frequency. A direct conversion receiver (DCR), also known as homodyne, synchrodyne, or zero-IF receiver, may then demodulate incoming signals by mixing the incoming signal with a local oscillator signal synchronized in frequency to the carrier signal. The baseband signal may then be obtained simply by low-pass filtering the mixer output, without requiring further detection.
A direct conversion transceiver may be implemented on a single chip, making it inexpensive and versatile. However, the transmission and receive paths for the base band signals (i.e., in-phase (I) and quadrature (Q)) are independently formed. Small variances in these paths introduce amplitude and phase variations in the respective transmit and receive signals, otherwise referred to as IQ imbalance impairments.
To calibrate a direct conversion transceiver, the impairments must be identified and compensated for prior to use. This compensation is difficult because it is necessary to calibrate the direct conversion transmitter and direct conversion receiver individually using a separate external reference for each path. If an uncompensated receiver is used to calibrate a transmitter over the complete frequency span, the transmitter calibration will be corrupted by the impairments of the receiver, and vice versa.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.